title: Analgesic alpha-conotoxins Vc1.1 and Rg1A inhibit N-type calcium channels in rat sensory neurons via GABAB receptor activation.
abstract: alpha-Conotoxins Vc1.1 and Rg1A are peptides from the venom of marine Conus snails that are currently in development as a treatment for neuropathic pain. Here we report that the alpha9alpha10 nicotinic acetylcholine receptor-selective conotoxins Vc1.1 and Rg1A potently and selectively inhibit high-voltage-activated (HVA) calcium channel currents in dissociated DRG neurons in a concentration-dependent manner. The post-translationally modified peptides vc1a and [P6O]Vc1.1 were inactive, as were all other alpha-conotoxins tested. Vc1.1 inhibited the omega-conotoxin-sensitive HVA currents in DRG neurons but not those recorded from Xenopus oocytes expressing Ca(V)2.2, Ca(V)2.1, Ca(V)2.3, or Ca(V)1.2 channels. Inhibition of HVA currents by Vc1.1 was not reversed by depolarizing prepulses but was abolished by pertussis toxin (PTX), intracellular GDPbetaS, or a selective inhibitor of pp60c-src tyrosine kinase. These data indicate that Vc1.1 does not interact with N-type calcium channels directly but inhibits them via a voltage-independent mechanism involving a PTX-sensitive, G-protein-coupled receptor. Preincubation with a variety of selective receptor antagonists demonstrated that only the GABA(B) receptor antagonists, [S-(R*,R*)][-3-[[1-(3,4-dichlorophenyl)ethyl]amino]-2-hydroxy propyl]([3,4]-cyclohexylmethyl) phosphinic acid hydrochloride (2S)-3[[(1S)-1-(3,4-dichlorophenyl)-ethyl]amino-2-hydroxypropyl](phenylmethyl) phosphinic acid and phaclofen, blocked the effect of Vc1.1 and Rg1A on Ca2+ channel currents. Together, the results identify Ca(V)2.2 as a target of Vc1.1 and Rg1A, potentially mediating their analgesic actions. We propose a novel mechanism by which alpha-conotoxins Vc1.1 and Rg1A modulate native N-type (Ca(V)2.2) Ca2+ channel currents, namely acting as agonists via G-protein-coupled GABA(B) receptors.
authors.affiliation: Queensland Brain Institute and School of Biomedical Sciences, and Institute for Molecular Bioscience, The University of Queensland, Brisbane, Queensland 4072, Australia.
authors.forename: Brid
authors.initials: B
authors.lastname: Callaghan
authors.forename: Alison
authors.initials: A
authors.lastname: Haythornthwaite
authors.forename: Géza
authors.initials: G
authors.lastname: Berecki
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Clark
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
authors.forename: David J
authors.initials: DJ
authors.lastname: Adams
mesh_terms: D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D000831:Animals, Newborn; D001418:Baclofen / Q000031:analogs & derivatives / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020864:Calcium Channels, N-Type / Q000502:physiology*; D002478:Cells, Cultured; D020916:Conotoxins / Q000494:pharmacology*; D004307:Dose-Response Relationship, Radiation; D004558:Electric Stimulation / Q000379:methods; D018756:GABA Antagonists / Q000494:pharmacology; D005727:Ganglia, Spinal / Q000166:cytology; D008564:Membrane Potentials / Q000187:drug effects / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D037342:Pertussis Toxin / Q000494:pharmacology; D010721:Phosphinic Acids / Q000494:pharmacology; D011412:Propanolamines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018079:Receptors, GABA / Q000502:physiology*; D011984:Sensory Receptor Cells / Q000187:drug effects*; D020960:omega-Conotoxins / Q000494:pharmacology
chemical_list: D000700:Analgesics; D002121:Calcium Channel Blockers; D020864:Calcium Channels, N-Type; D020916:Conotoxins; D018756:GABA Antagonists; D010721:Phosphinic Acids; D011412:Propanolamines; D018079:Receptors, GABA; C510079:conotoxin alpha-RgIA, Conus regius; D020960:omega-Conotoxins; C052329:phaclofen; C085075:CGP 55845A; D001464:Barium; C507383:alpha-conotoxin Vc1.1; D037342:Pertussis Toxin; D001418:Baclofen